Apparatus and Method for Preventing False Touches in Touch Screen Systems

• US 20140098032A1
• Filed: 10/09/2012
• Published: 04/10/2014
• Est. Priority Date: 10/09/2012
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Inventors: Nagarajan, Mythreyi, Bhatia, Ravi, Ng, HonSiong, Chandran, Praveesh
• Granted Patent: US 9,229,576 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment

Abstract

A method comprises during a frame period finding a first EFT noise influenced sensor of a touch screen panel, determining whether the first EFT noise influenced sensor is located at a last transmitting/driving line of the touch screen panel, designating the frame period as a noise influenced frame period using an absolute value threshold if the first EFT noise influenced sensor is not located at the last transmitting/driving line and designating the frame period as the noise influenced frame period using a percentage threshold if the first EFT noise influenced sensor is located at the last transmitting/driving line.

Claims

1. A method comprising:

in a frame period, scanning a touch screen panel from a first corner to a second corner, wherein;

the touch screen panel comprises a plurality of sensors arranged in rows and columns; and

the first corner is diagonally opposite to the second corner;

determining whether a sensor is affected by electrical fast transient (EFT) noise; and

considering a frame as a noise influenced frame if a total number of sensors affected by EFT noise is greater than a first noise threshold.

2. The method of claim 1, wherein:

the first corner is an upper left corner; and

the second corner is a bottom right corner.

3. The method of claim 1, the step of determining whether a sensor is affected by EFT noise further comprising:

setting a first threshold and a first hysteresis band, wherein the first threshold is less than a baseline of the touch screen panel;

comparing a signal generated by the sensor with the first threshold; and

labeling the sensor as a noise influenced sensor if signal strength of the signal exceeds the first threshold.

4. The method of claim 3, wherein:

the baseline is about 1000;

the first threshold is about 900; and

the first hysteresis band is from 900 to 950.

5. The method of claim 1, wherein:

the first noise threshold is 40.

6. The method of claim 1, further comprising:

finding a first noise influenced sensor;

determining whether the first noise influenced sensor is located at a last transmitting/driving line of the touch screen panel; and

determining whether a frame is a noise influenced frame by a second noise threshold.

7. The method of claim 6, further comprising:

finding all noise influenced sensors in the last transmitting/driving line of the touch screen panel;

calculating a percentage of noise influenced sensors over samples between the first noise influenced sensor and a last sensor of the last transmitting/driving line of the touch screen panel; and

considering the frame as a noise influenced frame if the percentage is greater than 60%.

8. A method comprising:

during a frame period, finding a first EFT noise influenced sensor of a touch screen panel;

determining whether the first EFT noise influenced sensor is located at a last transmitting/driving line of the touch screen panel;

designating the frame period as a noise influenced frame period using an absolute value threshold if the first EFT noise influenced sensor is not located at the last transmitting/driving line; and

designating the frame period as the noise influenced frame period using a percentage threshold if the first EFT noise influenced sensor is located at the last transmitting/driving line.

9. The method of claim 8, further comprising:

receiving raw signals from the touch screen panel; and

finding a first EFT noise influenced signal based upon a first predetermined threshold.

10. The method of claim 9, wherein:

the first predetermined threshold is a capacitance variation from a baseline of the touch screen panel.

11. The method of claim 10, wherein:

the first predetermined threshold is 900 when a baseline of the touch screen panel is 1000.

12. The method of claim 11, further comprising:

a hysteresis band around the first predetermined threshold.

13. The method of claim 8, further comprising:

finding a first EFT triggered touch point from a touch frame;

counting a total number of EFT triggered touch points; and

dropping the touch frame if the total number of EFT triggered touch points is greater than the absolute value threshold.

14. The method of claim 8, further comprising:

finding a first EFT triggered touch point in a last transmitting/driving line of a touch frame;

calculating a percentage of EFT triggered touch points over a sample from the first EFT triggered touch point to a last touch point of the last transmitting/driving line of the touch frame; and

dropping the touch frame if the percentage of EFT triggered touch points is greater than the percentage threshold.

15. The method of claim 14, wherein:

the percentage threshold is about 60%.

16. A system comprising:

a touch screen panel comprising a plurality of sensors arranged in rows and columns, wherein each sensor comprises;

a transmit node; and

a receive node, wherein the transmit node and the receive node form a capacitor;

a receiver coupled to the receive node; and

a processor coupled to the receiver, wherein the processor is configured to;

find a first EFT noise influenced sensor of the touch screen panel;

determine whether the first EFT noise influenced sensor is located at a last transmitting/driving line of the touch screen panel;

designate a touch frame as a noise influenced frame using an absolute value threshold if the first EFT noise influenced sensor is not located at the last transmitting/driving line; and

designate the touch frame as the noise influenced frame using a percentage threshold if the first EFT noise influenced sensor is located at the last transmitting/driving line.

17. The system of claim 16, wherein:

the processor receives raw data from the touch screen panel through the receiver.

18. The system of claim 16, wherein:

the touch frame is of 12 rows and 20 columns.

19. The system of claim 16, wherein:

the absolute value threshold is about 40; and

the percentage threshold is about 60%.

20. The system of claim 16, wherein:

the processor finds the first EFT noise influenced sensor by measuring signal strength a signal generated by the first EFT noise influenced sensor.